cpdf_setrgbcolor_fill

The document handle, returned by cpdf_open().

The red value, as a float between 0.0 (black) and 1.0 (red)

The green value, as a float between 0.0 (black) and 1.0 (green)

The blue value, as a float between 0.0 (black) and 1.0 (blue)